1. Field of the Invention
The present invention relates to a droplet jetting device, and particularly relates to a droplet jetting device for jetting droplets from nozzles of a recording head that is provided at a recording head section of an image forming device.
2. Description of the Related Art
Droplet jetting devices are common that supply liquid to a recording head provided at a recording head section of an image forming device, jet droplets of the liquid at a recording medium from nozzles, and cause an image to be formed. Examples of such droplet jetting devices include an inkjet recording device that jets ink from nozzles of an inkjet head. An example of a droplet jetting device that jets droplets from an inkjet head of this inkjet recording device is illustrated in FIG. 8.
In a droplet jetting device 120 shown in FIG. 8, a pressure of ink in an ink chamber inside an inkjet head 64 is controlled so as to be within a predetermined range. At times of starting and finishing image formation, the pressure of ink in the ink chamber changes greatly, because consumption of ink by the inkjet head 64 starts or finishes in an instant. Even when such load variations are severe, the ink pressure must be kept to within the predetermined range.
However, there is a problem as described below in regard to a pump P1 for supplying the ink and sensors S1 and S2 for monitoring the ink pressure.
In general, a tube pump is often used for the pump P1. In such a case, given a method of intermittently drawing on a tube filled with ink to feed out the ink, ripples (variations) of pressure are large. Moreover, because pump P1 itself is very expensive, it is not possible to dispose pump P1 in a vicinity of the inkjet head 64, which is packaged at high density. Therefore, pump P1 is disposed at a position away from the inkjet head 64, and a system has been adopted in which flow resistance of the ink tubing is utilized to moderate the ripples. However, because the flow resistance between the pump P1 and the inkjet head 64 is large, there are problems in that control responsiveness is poor and it is difficult to suppress the pressure changes just after starting or finishing image formation.
In addition, depending on the images to be formed, ink consumption amounts vary between plurally provided inkjet heads 64 and modules 65. Because ink is supplied in common to the head units, it is not possible to apply respectively separate controls thereto.
As for the pressure sensors S1 and S2, because the pressure sensors S1 and S2 themselves are ordinarily very expensive, it is not possible to provide the pressure sensors S1 and S2 at each of the inkjet heads 64. Therefore, a method of detecting pressures of ink in sub-tanks 128 and 132, which are distant from the inkjet heads 64, has been adopted. However, because there is flow resistance between the sub-tanks 128 and 132 and the heads, there is a problem in that it is difficult to accurately detect pressures of ink in vicinities of the inkjet heads 64, which is essentially what needs to be detected.
A technology is known that uses micro-pumps as pumps for supplying ink. Japanese Patent Application Laid-Open (JP-A) No. 2005-279784 describes a technology that uses micro-pumps based on actuators that employ MEMS (microelectromechanical systems) technology in micro-amount fluid jetting devices, which include inkjet printer heads. Further, a technology is known, in JP-A No. 2006-272577, in which an inkjet recording device supplies ink to a sub-ink tank with micro-pumps.
However, in the related art technologies mentioned above, simply using micro-pumps is described, which cannot deal with the problem of not knowing ink pressure in the vicinity of an inkjet head, which is essentially what needs to be detected, or the problem of it being difficult to suppress pressure changes immediately after starting or finishing image formation with good responsiveness.